106 
MEASUREMENT OF HIGH TEMPERATURES. 
[BULL. 54 
case the liquid sometimes bumps violently during ebullition. Tin 
liquid surface is at 10 cm from the bottom nearly. 
Table 13. — Constancy of temperature along axis of boiling tube. Mercury. T = 358° 
Height of 
j unction above 
bottom. 
t. 
e. 
T. 
Remarks. 
Cm. 
°C. 
Micro- 
volts. 
= 0. 
* C 5 
In liquid ? 
21.5 
21.5 
3320 
34!4 
347.4 
358.0 
1 
| 
r 11 
21.5 
3431 
357.0 
i Fresh mercury; brisk and regular 
j boiling. Liquid surface at 10 cm . 
I 12 
In vapors 
j 13 
21.5 
21.5 
3421 
3410 
356.2 
355.2 
1 15 
21.5 
3330 
348.2 
J 
In liquid-^ 8 
21.5 
3393 
353.9 
21.5 
3448 
358.4 
Fresh mercury; brisk and regular 
I 9 
21.5 
3436 
357.4 
> boiling. Liquid surface at 10 ri ". 
t 10 
In vapor i „ 
c lo 
21.5 
21.5 
3436 
3192 
357.4 
356.4 
Disks in the mercury tube. 
5 
24.0 
3425 
358.2 
) Violent boiling with bumping. 
15 
24.0 
3393 
325.3 
) Liquid surface at 10 cm . 

20.3 
3856 
391.3 
1 
5 
21.7 
3300 
345.8 
9 
23.6 
3436 
358.8 
10 
12 
15 
22.9 
23.4 
23.4 
3431 
3295 
3090 
357.8 
346.6 
329.1 
Gentle ebullition with bumping. 
Liquid surface at L0 am . 
20 
21.8 
745 
94.5 
25 
21.8 
443 
58.2 
30 
21.8 
317 
42.6 
J 
These tables show conclusively that for a distance along the central 
tube of about 1.5 cm above and below the surface of ebullition, the tempera 
ture is that of the boiling point of mercury, with an error of less thai 
a few tenths of a degree. The temperature of the liquid below the sur 
face and of the vapor above it depends on the position of the ring burnei 
and of the intensity of ebullition. The suddenness with which temper 
at ure decreases between 5 cm and 10 cm above the surface of ebullition is 
well shown by the data of the last part of Table 13. Hence it is per 
missible to speak of a zone of ebullition comprising in vertical extenl 
about 5 cm of the boiling tube above the surface. The use of loose disks 
or screens of asbestos in the boiling space, to guide the vapor or pre veil 1 
convection here, is of no obvious avail, probably from the great weighl 
of mercury vapor as compared with that of air. These disks complicate 
the apparatus, and are therefore to be discarded. Table 13 is an ex 
ample of many similar results. The two or three centimeters of avail 
able space for constant temperature are amply sufficient for the calibra 
tion and for many other purposes. At any given point of the space the 
constancy of temperature is almost jierfect. If the outside of the tube 
is well jacketed with asbestos wicking, the height of the space of con- 
(760) 
